Infants with inborn errors of bile acid metabolism and peroxisomal disorders, including Zellweger's syndrome and infantile adrenoleukodystrophy, commonly have liver disease because of impaired peroxisomal metabolism and accumulation of bile acid intermediates. Using techniques of mass spectroscopy, electron microscopy and MRI-spectroscopy, this study has evaluated the role of bile acid therapy (cholic acid) for liver disease with inborn errors of bile acid metabolism/peroxisomal disorders of infancy. During this study period, 1 additional patient with an inborn error of bile acid metabolism, 3-beta hydroxysteroid dehydrogenase/isomerase, was evaluated. Although rare disorders, study of these patients and the effects of bile acid therapy on the associated liver disease are extremely valuable. Since the initiation of this work on the CRC, two new inborn errors of bile acid metabolism have been identified, and our laboratories have also been involved in discovering an additional two defects in bile acid synthesis or conjugation. Worldwide, more than 50 subjects have now been found with defects in bile acid biosynthesis leading to hepatobiliary disease and/or severe fat and fat-soluble vitamin absorption.